The term “vertical-shaft kiln” designates any kiln of which the enclosure extends in a substantially vertical direction.
An installation for manufacturing a clinker usually has two objectives: to mass manufacture a clinker and manufacture a regular, that is to say a homogenous clinker.
It is known from the state of the art an installation for manufacturing a sulfo-aluminous clinker equipped with a cyclone preheater, a precalciner and a rotary kiln. Such an installation allows mass production but not the production of a regular clinker.
It is known, by document FR2928643, an installation for the manufacture of a sulfo-aluminous clinker equipped with a vertical-shaft kiln for decarbonatation and a continuous clinkering kiln.
The vertical-shaft kiln comprises an enclosure inside which a raw mix is poured containing in particular calcium, aluminum, silica, iron and sulfur in combined mineral form such as for example oxides, hydroxides, carbonates, chlorides or sulfates. The vertical-shaft kiln comprises supply furnace flues of a gas at a temperature ranging between 900° C. and 1150° C., in such a manner as to dehydrate and decarbonate the raw mix.
The continuous kiln comprises a furnace, inside which a plurality of moveable carriages circulate. One layer of raw mix from the vertical-shaft kiln is extended over each of the carriages. The continuous kiln comprises a plurality of burners distributed along the furnace. These burners take the raw mix to a temperature in the range of 1250° C. to 1450° C., in such a manner as to clinker it.
Such an installation allows to finely monitor the profile of temperatures during the clinkering by adjusting the power of the burners and the speed of displacement of the carriages. Thus, the manufactured clinker exhibits a very good regularity.
However, the thickness of the layers of raw mix disposed on the carriages of the continuous kiln is low. Moreover, the production capacity of such an installation is limited.
It is also known, by document CN1094383, an installation for the manufacture of a sulfo-aluminous clinker equipped with a vertical-shaft kiln. This vertical-shaft kiln comprises a furnace inside which is poured a raw mix containing calcium, aluminum, silica, iron, and sulfur mixed with a solid combustible such as coal.
A drawback of such an installation is that the raw mix exhibits an irregular granulometry. In addition, when this raw mix is poured into the furnace, the air circulates in unequal quantity between the pellets forming the raw mix, and the combustible is mixed in a heterogeneous manner. Thereafter, the combustion of the combustible is unequal, and the achieved clinker is irregular.
Furthermore, the proximity of the combustible and the raw mix pellets causes the formation of reducing zones in the furnace, that is to say zones without oxygen. These reducing zones lead to the loss of sulfur and a degradation of the chemical composition sought. Particularly, a C12A7 phase, called mayenite, appears. This phase highly accelerates the hydraulic setting up of a cement, and is consequently detrimental.
Finally, a vertical-shaft kiln, of the type described in document CN1094383, is generally provided with an ambient air inlet mouth in lower portion of the furnace.
Such a mouth allows the intake of combustion air of the solid combustible mixed with the raw mix.
Such a mouth further allows the cooling of the clinker before extraction from the furnace. On the other hand, the sticking risks, and after the blinding of the furnace, by the clinker may be limited.
A drawback of such a type of vertical-shaft kiln is that the cooling is undergone rather than mastered. However, it is known that the cooling speed of the clinker determines the setting up time and the demand for water of the cement achieved based on this clinker.
As a result, a cement achieved from a clinker manufactured in this type of kiln exhibits a badly mastered setting up time and demand for water.